A turbogenerator having a polyphase synchronous generator is normally used to produce electrical energy in a power station. The turbogenerator essentially comprises a gas turbine, a polyphase synchronous generator and an exciter current device, possibly as well as a steam turbine. The polyphase current which is produced by the generator is tapped off on the stator winding of the generator, while the rotor winding is excited with direct current to produce a magnetic field. It is known for the direct current to be provided via brushless rotating rectifier exciter machines, or via sliprings from a solid-state thyristor-controlled exciter device. A brushless rectifier exciter machine having external poles is coupled to the generator such that its rotor rotates with the generator shaft. In a situation such as this, the polyphase current which is first of all produced in the exciter machine can be rectified with the aid of rectifiers which rotate with the rotor shaft of the exciter machine. The direct current which is produced by a rectifier exciter machine such as this can be passed directly to the rotor of the generator, without sliprings.
In contrast to a turbogenerator having a steam turbine as a drive, a gas turbine cannot accelerate the turbogenerator on its own. In general, the turbogenerator is started up from so-called turning operation at a rotation speed of about 100 rpm to 200 rpm, for which purpose a hydraulic-oil drive is generally used. As is known, a gas turbine cannot be ignited until an adequate rotation speed of about 1000 rpm is reached and then being accelerated further up to the nominal rotation speed. A separate so-called starting motor can be used to reach this rotation speed limit, or the generator can be used as a frequency-control motor for acceleration.
The shaft runs in those power stations which comprise a steam and/or gas turbine as well as a generator, must be rotated at a low rotation speed after being decelerated from operation at rated rotation speeds, and this is also referred to as a turning, in order to prevent deformation of the shafts as they cool down.
In this case, the shaft run is moved by a hydraulic motor, which is operated by oil pressure and is designed for this purpose, at rotation speeds of about 2 rpm up to 70 rpm.